Vehicle cooling systems generally include a belt driven water pump with a belt driven shaft and shaft mounted impeller to drive coolant through the system. Typically, a pump housing is detachably connected to the engine block and a shaft supporting bearing assembly is press fitted within a sleeve of the housing. It is also known to integrate the outer race of the bearing assembly with the pump housing, which, at least theoretically, has the potential to reduce cost and complexity by eliminating a part. An example may be seen in U.S. Pat. No. 3,981,610. Such integrated pump housing and bearing assemblies have found little or no practical production use, however. This is because a steel suitable for a bearing race and pathway must be quite hard. Conversely, a typical pump housing is relatively large and includes complex, passage defining curvatures, and must be formed of a soft steel to be easily stamped.
The greatest challenge in the design vehicle water pumps, however, is universally recognized to be sealing, a problem which has still not been solved to the industry's complete satisfaction. It is possible to use a magnetic impeller driving means which needs no seal. However, a magnetic drive means is, as yet, relatively costly. When a conventionally driven impeller is used, some type of rubbing seal must be used, since the impeller driving shaft must physically extend into the pump housing. The location where a seal must be placed is the space between the shaft support bearing and the shaft impeller. Any seal in that location inevitably sees the hot and corrosive coolant, which is very detrimental to common seal materials. The standard industry water pump seal includes two basic parts, a sealing ring, and a sealing element with a wear face that the sealing ring runs against. One part of the seal is mounted to the pump housing-bearing structure, and the other to the impeller-shaft structure. Therefore, in addition to the corrosive, hot coolant, the sealing ring wear face interface sees the considerable heat of friction of the very rapid relative shaft-bearing rotation. Because of the inevitable wear at this interface and the high pressure of the hot coolant, it has also been found necessary to spring bias the ring and wear face together to maintain firm contact, which increases the heat of friction.
The standard industry response to the sealing problem has been to make the wear face from a non corroding ceramic material, and to make the sealing ring of a differing non corroding material, such as carbon. However, ceramic itself presents so many practical problems that the majority of issued patents in the art seem to deal almost exclusively with proposed solutions to the inherent difficulties of using ceramic. Ceramic is brittle, very subject to thermal shock, difficult to lap to a flat surface, and extremely difficult to structurally mate with the steel components of the rest of the pump. For example, U.S. Pat. No. 3,782,735 proposes putting a tight metal band around the ceramic sealing element to try to maintain its structural integrity. To mate the ceramic to the metal impeller shaft, an elastomer isolator is used, which would allow the ceramic ring to wobble, potentially threatening the alignment and integrity of the sealing interface. The elastomer also acts as an insulator, preventing the ceramic from shedding the heat of friction. The ceramic seal element is better handled in the pump design disclosed in U.S. Pat. No. 3,895,811, also assigned to the assignee of the present invention. There, the ceramic element is firmly set into and held by surrounding deformable metal washers, which keeps the ceramic square to the other part of the seal, and which provides better heat dissipation. However, cost considerations have prevented production adoption of this design, and the conventional seal of the type described is very widely used.